The Lore Concerning Places
The dindsenchas are an example of what is called onomastic literature--in this case, relatively short poems which describe how places in Ireland got their name.
Often, these "explanations" are made to fit the name, and not the other way around, as the place-name was much older than the Middle Irish spoken at the time of the poems' composition.
Most of the dindsenchas are contained in the Book of Leinster. They were translated at the turn of the 20th century by E. J. Gwyn. A five volume set of Gwyn's translation can be purchaced at: Http://www.veryfaery.com/dindsenchas.html
Examples of dindsenchas: Tlachtga, Temhair.
Celtic Mythology & Medieval Celtic Manuscripts
Early Irish Literature Guide:
Mythological Cycle | Ulster Cycle | Fionn Cycle | Cycle of the Kings
Saints' Lives | Independent Narratives | Dindsenchas | Banshenchas